Threaded intraosseous dental implant

ABSTRACT

The screw-type intraossal dental implant has a bottommost implant tip that is located in the apical area and comprises a root part which extends up to said implant tip and which is intended for insertion into a jaw bone. The implant neck extending up to the coronal area is placed on the root part and is intended for being placed inside the gingivae. The outer thread on the root part is preferably self-cutting. The invention is characterized in that the root part comprises an essentially parabolic outer contour with the implant tip serving as the vertex. The inventive outer contour makes it possible to obtain an improved primary stability and guarantees, to a great extent, the long-term success of the implant.

FIELD OF APPLICATION OF THE INVENTION

The present invention relates to a dental implant which is intended tobe fitted in the jawbone and which has a thread on its outside. To thisextent, the implant according to the invention differs generically fromblade and cylinder implants as the other forms of intraosseous dentalimplants. In particular, the invention concerns the outer geometry ofthe implant, the measurement ratios of the implant body, and thecharacteristics of the outer thread, with the object of improving bothprimary and secondary stability and of thereby guaranteeing thelong-term success of fitted implants.

PRIOR ART

Although this invention concerns dental implants, the shorter form“implant” will be used hereinafter for the sake of brevity. An overviewof the implant forms commonly used in dentistry is given by H.Spiekermann in “Implantologie, Farbatlanten der Zahnmedizin” publishedby Georg Thieme Verlag Stuttgart and New York, 1994, vol. 10, page 15.Here, a differentiation is made between blade, cylinder and screwimplants. The blade implants which may possibly be advantageous for veryspecific applications are not considered at all. The cylinder implantshave a cylindrical body which is either continuous or stepped. The rootpart can have openings for better bone integration, and the implant tiplying at the apical end has the shape of a semisphere or a roundedsummit. The root part has a rough or profiled surface produced bymaterial application or removal. The implant neck or head is in mostcases smooth.

The screw implants have an outer thread extending at least over most ofthe root part. Their implant bodies are likewise cylindrical with asemispherical, rounded, frustoconical or parabolic implant tip (see U.S.Pat. No. 4,626,214). Slightly conical forms are also known (see U.S.Pat. No. 4,713,003). The implant necks are in most cases alsocylindrical at the transition from the root part, whereas in the coronaldirection the heads taper conically, widen in a trumpet shape or have anexternal polygon.

The basically cylindrical shape of the root part has proven not bestsuited for obtaining the desired postoperative primary stability of thefitted implant. Moreover, the lifetime of the implants is in many casesinadequate: the fitted implant loosens early after just a few years.Investigations revealed that this early loosening is caused by boneresorption around the fitted implant, which is attributable toinsufficient introduction of force to the bone via the existing implantforms. Bone expansions of between 1000 and 4000 microstrains are definedas relevant to remodeling. Values below 1000 microstrains are consideredinadequate and result in reduced mineralization and formation ofconnective tissue. Values above 4000 microstrains are consideredexcessive and result in bone resorption (see Barbier, L. et al.: Finiteelement analysis of nonaxial versus axial loading of oral implants inthe mandible of the dog, in J. Oral Rehabil. 1998, 25(11):847-858).

OBJECT OF THE INVENTION

In view of these shortcomings of the dental implants known to date, itis an object of the invention to propose an implant form whichcontributes to increasing the primary stability of fitted implants sothat the implant is immediately able to bear loads, both during thepostoperative work involved in attaching the superstructures and alsoduring use by the patient. Immediate ability to bear loads signifies theprimary stability achieved immediately after implantation. However, itwill be appreciated that in some cases it is advantageous to waitseveral days of the main wound-healing phase before actual loading ofthe implant. Moreover, an optimized implant form is intended to maintainthe natural introduction of force into the bone, comparable to that in areal tooth, and thereby to guarantee the long-term success to a greaterextent.

SUMMARY OF THE INVENTION

The dental implant has a bottommost implant tip located at the apex anda root part which extends to the implant tip and is intended to befitted in the jawbone. Adjoining the root part there is the implant neckwhich extends in the coronal direction and, in the implanted state,comes to lie inside the gingiva. At least over some of the root part,the implant is provided with an outer thread, which can be self-cutting.The main feature is that the root part has a principally parabolic outercontour with the implant tip as vertex.

The description given below relates to preferred illustrativeembodiments of the invention.

The root part and the implant neck adjoin each other on a theoreticalridge line, the root part having the maximum length l_(max) extending inthe axial y-direction. At the ridge line, the root part has the maximumradius r_(max) extending in the radial x-direction. Placed in aCartesian system of x-y coordinates, and with the implant tip positionedat the origin of this system, the parabolic outer contour follows theequationl _(y) =K·4r _(x) ², with:

-   -   l_(y) as the respective ordinate value;

r_(x) as the associated abscissa value; and

K as the constant resulting from the equation

 K=l_(max):4r_(max) ².

The maximum radius r_(max) is between 1.0 mm and 3.0 mm; it preferablylies in the range of from 1.5 mm to 2.0 mm. The maximum length l_(max)of the root part correlates with the pitch of the outer thread, thelatter ending at a distance from the ridge line. The distance ispreferably 1.0 mm to 4.0 mm. This distance is defined by the thicknessof the cortical zone on the marginal bone and by the length of theimplant. In order to guarantee an optimum introduction of force into thebone in this area, the distance of the outer thread from the ridge linebecomes greater as the length of the root increases. In addition, thedistance contributes to excluding the very critical entry of bacteriainto the implant bed.

At the root part, and extending in the y-direction, the thread teethhave a height in the region of 0.3 mm; and, extending in thex-direction, a length in the range of from 0.25 mm to 0.5 mm. The lengthof the m thread teeth decreases as the maximum length of the root partincreases.

The implant is made of biocompatible material having suitable stabilityproperties. Examples of these are titanium, titanium-based alloys, othermetals or metal alloys, ceramic, glass ceramic or ceramic-likematerials, and biocompatible plastics. The root part has a rough surfacewhich is, for example, plasma-coated or ceramic-coated, or has beentreated, for example, chemically, electrochemically, mechanically or bylaser. An implant neck made of titanium or a titanium-based alloy ispolished. The implant neck can also be coated with ceramic or withceramic-like material or with hydroxyapatite. Measured in they-direction, the implant neck has a height in the region of 2.0 mm andis cylindrical or widened or narrowed in a trumpet shape or conically inthe coronal direction. The dental implant can be used either as aone-phase or two-phase implant.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

FIG. 1 shows a front view of an implant according to the invention;

FIG. 2 shows the implant according to FIG. 1 in a system of x-ycoordinates; and

FIG. 3 shows an enlargement of the detail X from FIG. 1.

EMBODIMENT

There follows a detailed description of an illustrative embodiment ofthe dental implant according to the invention, with reference to theattached drawings.

At the very bottom of the implant is the apically situated implant tip 1to which the root part 2 extends from the coronal direction, which rootpart 2 is intended to be fitted in the jawbone. Adjoining the top of theroot part 2, at the theoretical ridge line 5, is the implant neck 3which extends in the coronal direction and is intended to lie inside thegingiva. From the implant tip 1 to a point below the ridge line 5, theroot part 2 is provided with an outer thread 4 which is preferablyself-cutting and has the pitch S. The outer thread 4 ends at a distancebelow the ridge line 5; the distance is preferably in the range of from1.0 mm to 4.0 mm. The root part 2 has a substantially parabolic outercontour A with the implant tip 1 as vertex.

The following dimensions can be defined on the implant:

-   -   l→total length, for example 12.0 mm, extending in the axial        y-direction, on the ordinate axis;    -   l_(max)→part of the total length l and maximum length of the        root part 2;    -   h→apart of the total length l and height of the implant neck 3;    -   r_(max)→maximum radius of the root part 2 at the ridge line 5,        extending in the radial x-direction, on the abscissa axis;    -   d→nominal diameter of the implant, which is derived from        2·r_(max);    -   g_(h)→height of the thread teeth 40 of the outer thread 4 on the        root part 2, extending in the y-direction;    -   g_(l)→length of the thread teeth 40 in the x-direction.

If the implant is placed with its parabolic outer contour A in aCartesian system of x-y coordinates and the implant tip 1 is positionedin this case at the origin of the system of coordinates, the outercontour A follows the equation l_(y)=K·4r_(x) ². Here represent:

-   -   l_(y)→the respective ordinate value for forming the outer        contour A;    -   r_(x)→the abscissa value associated with the ordinate value        l_(y), and    -   K→the constant which results from the equation        K=l_(max):4r_(max) ².

The maximum radius r_(max) is between 1.0 mm and 3.0 mm, preferablylying in the range of from 1.5 mm to 2.0 mm. Thus, assuming for examplethat r_(max)=2.0 mm (nominal diameter of the implant d=4.0 mm), thisgives the following values for the constant K and for the equations fordetermining the ordinate values l_(y) and abscissa values r_(x) of theouter contour A:

Length l_(max) of root part [mm] l_(y); r_(x) Constant K 6 l_(y) = K ·4r_(x) ² 0.375 8 l_(y) = K · 4r_(x) ² 0.500 10 l_(y) = K · 4r_(x) ²0.625 12 l_(y) = K · 4r_(x) ² 0.750 14 l_(y) = K · 4r_(x) ² 0.875 16l_(y) = K · 4r_(x) ² 1.000

The maximum length l_(max) of the root part 2 correlates with the pitchS of the outer thread (4).

Thus, assuming for example that r_(max)=2.0 mm (nominal diameter of theimplant d=4.0 mm) and assuming maximum lengths l_(max), this gives thefollowing relations for the pitch (S) of the outer thread 4:

Length l_(max) of root part [mm] Pitch (S) [mm] 6 0.65 8 1.00 10 1.00 141.00 16 1.00

The outer thread (4) at the root part (2) with its thread teeth (40) hasthe following values, for example:

-   -   extending in the y-direction, a height g_(h) of the thread teeth        40 in the region of 0.3 mm; and    -   extending in the x-direction, a length g_(l) of the thread teeth        40 in the range of from 0.25 mm to 0.5 mm.

The length g_(l) of the thread teeth 40 decreases as the maximum lengthl_(max) of the root part 2 increases.

Thus, assuming for example r_(max)=2.0 mm (nominal diameter of theimplant d=4.0 mm), this gives the following values for the outer thread4 with its thread teeth 40:

Height g_(h) Length g_(l) Length l_(max) of of thread of thread rootpart [mm] teeth [mm] teeth [mm] 6 0.30 0.40 8 0.30 0.40 10 0.30 0.30 140.30 0.25 16 0.30 0.25

The implant is made of biocompatible material having suitable stabilityproperties. Examples are titanium, titanium-based alloys, other metals,their alloys, ceramic, glass ceramic or ceramic-like materials, andbiocompatible plastics. The root part 2 has a rough surface which, forexample, is plasma-coated or ceramic-coated or is treated, for example,chemically, electrochemically, mechanically or by laser. An advantageoussurface structure for the root part 2 is the subject of the invention inPCT publication WO 99/13700. The implant neck 3 can be made of titanium,a titanium-based alloy, another biocompatible metal or alloy and willthen advantageously be polished. The implant neck 3 could be coated withceramic, glass ceramic, ceramic-like material, hydroxyapatite, plasticor metal.

The implant neck 3 has, in the y-direction, a height h in the region of,for example, 2.0 mm. It is cylindrical or widens or narrows in a trumpetshape or conically in the coronal direction.

1. A dental implant comprising: a) a bottommost implant tip located atan apex; b) a root part which has a length, extends to the implant tip,is intended to be fitted in a jawbone, and has a parabolic outer contourwhich, when placed in a cartesian system of x-y coordinates, with theimplant tip positioned at the origin, follows the equationl_(y)=K·4r_(x) ², where l_(y) represents a y coordinate value and r_(x)represents an x coordinate value, and the constant K results from theequation K=l_(max)/4r_(max) ²; c) an implant neck adjoining the rootpart, which extends in a coronal direction and is intended to lie insidethe gingiva; and d) an outer thread having a pitch and provided on theroot part, wherein the root part has the parabolic outer contour alongall of the length of the root part and as far as a theoretical ridgeline at which the root part adjoins the implant neck, the root part atthe ridge line having a maximum radius extending in a radial direction.2. The dental implant as claimed in claim 1, wherein the outer threadprovided on the root part has an outer contour extending parallel to theparabolic outer contour of the root part, and ends at a distance of 1 mmto 4 mm from the ridge line.
 3. The dental implant as claimed in claim1, wherein the maximum radius is between 1 mm and 3 mm.
 4. The dentalimplant as claimed in claim 3, wherein the maximum radius is from about1.5 mm to about 2 mm.
 5. The dental implant as claimed in claim 1,wherein a) the outer thread is self-cutting; b) the length of the rootpart and the pitch of the outer thread correlate with one another asfollows: Length of root part (mm) Pitch (mm) 6 0.65 8 1 10 1 14 1 16 1

when the maximum radius of the root part at the ridge line is equal to 2mm; and c) the outer threads ends at a distance in the y-direction offrom 1 mm to 4 mm from the ridge line.
 6. The dental implant as claimedin claim 1, wherein a) the outer thread includes thread teeth, b) thethread teeth at the root part extend in a y-direction, and have a heightof about 0.3 mm; and c) the thread teeth, in an x-direction, have alength in the range from 0.25 mm to 0.5 mm.
 7. The dental implant asclaimed in claim 6, wherein a) the maximum radius is equal to 2 mm; andb) the thread teeth have the following values relative to the length ofthe root part: Length of Height of thread Length of thread root part(mm) teeth (mm) teeth (mm) 6 0.3 0.4 8 0.3 0.4 10 0.3 0.3 14 0.3 0.25 160.3 0.25.


8. The dental implant as claimed in claim 1, wherein a) the implant ismade of biocompatible material; and b) the root part has a rough surfacewhich is treated by one selected from the group consisting ofplasma-coating, ceramic-coating, chemical treatment, electrochemicaltreatment, mechanical treatment, and laser treatment.
 9. The dentalimplant as claimed in claim 8, wherein the biocompatible material isselected from the group consisting of titanium-based alloys, metals,metal alloys other than titanium-based alloys, ceramic, and plastic. 10.The dental implant as claimed in claim 1, wherein the implant neck ispolished and is made of a material selected from the group consisting oftitanium, a titanium-based alloy, a biocompatible metal , and abiocompatible metal alloy other than titanium-based alloys.
 11. Thedental implant as claimed in 1, wherein a) measured in a y-direction,the implant neck has a height in the range from 1 mm to 3 mm; and b) theimplant neck is cylindrical in the coronal direction.
 12. The dentalimplant as claimed in claim 1, wherein the implant neck is polished andcoated with a material selected from the group consisting of ceramic,glass ceramic, hydroxyapatite, plastic, and metal.
 13. The dentalimplant as claimed in 1, wherein a) measured in a y-direction, theimplant neck has a height in the range from 1 mm to 3 mm; and b) theimplant neck has a dimension transverse to the coronal direction thatchanges in the coronal direction.